1. Field of the Invention
This invention relates generally to optical elements for converting collimated light beams into light planes, and relates more particularly to the use of such optical elements in self-leveling surveying, leveling, and/or plumbing instruments for projecting horizontal and/or vertical light planes onto reference objects.
2. Description of Related Art
Conventional self-leveling instruments for projecting horizontal and/or vertical light planes onto reference objects utilize lasers and cylindrically-surfaced lenses to generate horizontal and/or vertical planes, of light. U.S. Pat. No. 5,539,990, U.S. Pat. No. 5,243,398, and Japanese Application No. 1991-90270 (Public Disclosure No. 1993-40815), published Jun. 1, 1993, disclose three such instruments. Unfortunately, as shown in FIG. 4, when such cylindrical lenses are used to project a light plane onto a wall, floor, ceiling, or other reference object as an illuminated line 10, the distal edges of the line 10 (top and bottom edges as shown in FIG. 4) fade as they extend farther away from the point on the wall that is coaxial to the input collimated light path. This makes it more difficult or impossible to see the distal extremities of the line 10. In some conventional designs, the distal extremities of the light plane are simply blocked off within the instrument, thereby wasting the cut-off portion of the light.